Shearing Recommendations

How many inches should a tree be cut?
What do lateral branches do to the trunk?
What process directs the shape of the tree?

Transcription

1 Shearing Recommendations North Central Regional Extension Publication No. 310 for Christmas Tree Producers Over the past several years, Christmas tree production has become a significant industry in much of the north central United States. Established growers have expanded their production and new growers have entered the business. Today several thousand Christmas tree producers manage plantations in many counties through the region. Operations range from a few acres managed for cut-your-own markets to large acreages producing trees exclusively for the wholesale market. Regardless of the size of the operation, management practices have become more sophisticated as growers attempt to increase both the quantity and the quality of production while holding production costs at acceptable levels. As the Christmas tree industry has intensified its tree management practices, the marketplace has likewise become more demanding. Tree quality has become a principal concern for both growers and consumers. Increasingly, higher quality trees are required to maintain sales in a very competitive market. Many factors contribute to tree quality. One of the most important during the production period is proper shearing. This bulletin suggests some ways to improve the quality of shearing and thereby contribute to the production of duality trees. Objectives of shearing Shearing is done to regulate and direct the growth of individual trees. The objectives are to develop a symmetrical shape, which is characteristic of quality trees, and to increase foliage density, which will result in a fuller tree with uniform foliage. Though some variation in the shape of trees is permitted both by USDA grading ~' standards and by consumer preferences, the ideal tree has a "two-thirds taper"; that is, the base of the tree is two-thirds as wide as the height. For a tree 6 feet tall, the width of the base would not exceed 4 feet. Other degrees of taper are permitted (Fig. 1 ), though market demand for both narrow and wide trees is lower. Acceptable tapers will vary to some degree by species; wider tapers are more acceptable for pines than for true firs, spruces and Douglas fir.

2 Tree response to shearing As indicated, the purpose of shearing is to direct the growth of branches and foliage so the shape and the amount of foliage developed will be acceptable. The shearing technique needed to reach these objectives varies by species group. Pines respond differently than spruces, firs or Douglas fir. When pine branches produced in the current growing season are cut, new buds develop at the bases of needle fascicles near the cut ends. Normally five to seven buds develop on an uncut branch, but 10 to 18 buds will form- in response to cutting. Cutting the branches directs the shape of the tree, and the additional buds will develop into twigs that will increase foliage density. New bud formation is best on twigs produced during the current growing season; however, cuts made into older (second-year) tissue will also result in buds. Shearing into this older tissue is usually not necessary if annual shearing has occurred. To obtain maximum bud development, shearing must occur during the active growing season. Shearing at other times will result in branch dieback and misshapen trees. Douglas fir, the true firs and spruces respond differently to shearing. These species are characterized by lateral buds along the twigs in addition to> a terminal bud cluster. When a branch is cut during shearing, new buds do not form at the bases of the needles, as with pines. Rather, the lateral bud nearest the cut surface assumes dominance and the new terminal or lateral branch tissue develops from this point. Shearing of these species should Fig. 2. Some of the common tools and equipment used to trim and shape Christmas trees. be delayed until late summer when branches have stiffened and bud formation is complete. Shearing tools and equipment Several types of tools and/or equipment are used to shear Christmas trees (Fig. 2). These include hand clippers, hedge clippers and shearing knives. A leg guard should also be considered part of shearing equipment. Besides hand equipment, some mechanically powered trimmers are also available (Fig. 3). Power trimmer use is restricted by tree size, terrain and condition of the plantation (weeds, tree Fig. 3. Mechanical l Christmas tree shearing units can increase the number of trees sheared each day. spacing, furrows, etc./. Choice of shearing equipment depends on the species of tree, the age of the tree and individual preference. Many growers use one type of tool (e.g., hedge clippers) when trees are small but another (knives) for older trees. Shearing equipment must be kept clean. Accumulated pitch on clippers and knives increases the difficulty of shearing and can become a safety hazard. Detergent solutions, mineral spirits and petroleum distillates are effective cleaning agents. Steel wool is commonly used with these solutions to remove accumulated pitch. Teflonbased or other non-toxic lubricants should be used on mechanical trimmers after cleaning. Other lubricants can dry or burn the remaining foliage on the sheared tree. Time of- shearing The proper time for shearing depends on the species and the growing location within the region. Pines - including Scotch, white, red and Austrian - should be sheared during the active growing season when terminal growth is nearly complete. In the southern portion of the region, this usually occurs between June 1 and 10; in the more northerly states, shearing begins between June 20 and 30. Shearing can continue through mid-july to early August, depending on location, but most growers plan on being finished by August 1 at the latest. Late shearing results in the development of fewer and weaker buds. Likewise, shearing too early (late May to early June, depending on location/ results in the production of too many buds, which can develop into weak and often spindly branches. A summary of suggested shearing

3 TABLE I. Suggested shearing schedule., DATE TREE AGE RECOMMENDED ACTIONS PINES SPRUCES - FIRS June 1-2 Remove multiple stems, - July 30 cut terminal to 12 inches, if necessary. June 1-3 Trim terminal to 12 - July 30 inches, cut back lat erals, remove lower branch whorls to form a handle. Aug Remove multiple May 1 stems, cut terminal to 12 inches, remove lower branches to form a handle. June Cut terminal to 12 - July 30 inches, trim laterals to develop a two thirds taper, com plete corrective pruning as necessary. Aug. 1-4 to year -- Cut terminal to 12 May 1 before inches, trim laterals harvest to develop a two thirds taper, remove multiple stems that may develop. June 1 - Year of Cut terminal to 12 - July 30 harvest to 15 inches, lightly trim laterals as necessary to main tain shape Aug. 1 - Year of -- Cut terminal to 12 to Sept. 1 harvest 15 inches, lightly trim laterals as necessary to maintain shape times and activities is presented in Table I. Within the pines, longer-needled species such as red and white pines should be sheared early in the shearing period. Buds on these species are slower to develop than those on Scotch pine. Earlier shearing of these species provides more time for bud formation and development, thereby contributing to fuller branch development the following spring. Because of differences in bud location and plant response, shearing of Douglas fir, the true firs and spruces begins at the end of the active growing season (late July and early August) and continues through the dormant season. Some evidence suggests that bud vigor and twig growth the following growing season will be better if shearing is done during late summer and early fall rather than the following spring before growth begins. Guidelines for shearing pines The shaping/shearing process for pine species should begin in the second growing season after planting. Examine each tree and remove double or multiple tops. The remaining terminal shoot should be cut back to a maximum length of 12 to 14 inches. Little, if any, shearing of side branches should occur. The basal branches on each tree should be removed to form a handle to accommodate the tree stand. Usually I inch of handle should be present for each foot of tree height at maturity. All branches up to this height (8 to 10 inches) or to the first complete whorl of lateral branches should be removed. In the third growing season, shear both the terminal leader and the lateral branches of the tree. Begin by cutting the terminal leader to a length of 12 to 14 inches, or less if the lateral whorl immediately below the terminal is not strong and vigorous. The cut on the terminal branch should be made at an approximate 45 degree angle so needle fascicles on one side will be higher than those on the other (Fig. 4). This practice will favor the development of a new terminal bud in a position where terminal dominance can be expressed. This will contribute to the development of a straight stem. The lateral branches of the terminal whorl are then cut so they are approximately two-thirds as long as the terminal shoot (Fig. 5). Following cutting, the line established by the relationship between the top of the terminal shoot and the ends of cut lateral branches of the terminal whorl is extended downward to determine where other lateral branches should be cut (Fig. 6). Minimal shearing of lateral branches in the first few years is recommended. The aim is to remove only excessively long branches. Many growers

4 Fig. 4. Cutting the terminal leader at an approximate 45 degree angle will favor development of a new dominant terminal bud. will shear trees in the third and fourth growing seasons to develop an 85 to 90 percent taper. This is done to develop. width in the tree -in later growing seasons, lateral growth of the lower branches will be considerably less than on upper brandies. If shearing of the sides is "too tight" early in the life of the tree, trees with a narrow or candlestick taper are likely to result. This is especially likely if the trees are allowed to grow to heights taller than 7 feet. In the fourth and later growing seasons, shearing continues in much the same manner as in year three. The length of the terminal shoot should not exceed 12 inches. Cutting of the laterals.will follow the taper relationship established by the terminal and top laterals. It is important to maintain straight sides on the tree and avoid rounded or bullet-shaped trees /Fig. 7/. These result from failure to cut the laterals on the upper portion of the tree short enough in relation to the length Fig. 5. Lateral branches of the terminal whorl are cut so they are about two-thirds as long as the terminal leader. of the terminal. Trees so sheared appear unnatural and are not as well accepted in the marketplace as are more symmetrically shaped trees. In the year of harvest, shearing should be minimal. Trees are more natural looking and marketable if only light trimming is done. The basic shape of the tree will have been determined by past shearing activities. Shearing cuts at this time should be light, removing only those lateral branches that extend beyond the general outline of the tree. If multiple terminal shoots are present, they should be thinned to one centrally located branch. Usually the terminal branch will be left a little longer than it had been in previous years. It should not exceed 15 inches in length, however. Growers do not agree whether trees should be sheared early or late during the shearing period in the harvest year. Some growers will complete the shearing of non-harvestable trees before shearing those to be harvested. They do this because they believe that bud set following shearing will be better if trees are sheared earlier rather than later. Obviously, bud set on trees to be harvested need not be particularly full or complete. Other growers will shear trees to be harvested early so that budset, needle elongation and coverage of the cut twig ends can occur to the fullest, thereby making the tree look as natural as possible. Unless shearing is done late (after Aug. 1 /, it is probable that needle elongation and bud set will be adequate to provide a natural appearance. Guidelines for shearing firs and spruces As indicated earlier, growth patterns and twig-bud anatomy are different for these species than for pines. The branches of spruces and firs, including Douglas fir, are characterized by the presence of single needles

5 Fig. 6. Correct location of lateral shearing cuts as determined by the relationship between the length of the terminal leader and lateral branches of the terminal whorl. and lateral buds located along the twig. As previously mentioned, when branches are cut during shearing, new buds do not form at the bases of needles. Rather, the lateral bud nearest the cut twig end will assume dominance, and growth the following growing season will begin from this point. For this reason, the time of shearing is not as critical for these trees as for pines. Shearing for spruces, firs and Douglas fir usually begins in late July or early August and may continue through fall, winter and early spring. Shearing for newly established plantations should begin during the third growing season after planting. Each tree should be examined, and double terminal branches and double stems removed. Basal pruning to form a clean handle should also be completed. If a symmetrical growth pattern is developing naturally in the tree, little, if any, shearing will be necessary at this time. In the fourth and later years, shearing should concentrate on maintaining a central leader (terminal branch) and symmetrical tree shape. Unless excessive terminal growth has occurred / 15 inches or more), the terminal shoot should not be cut as long as full lateral branch development is occurring. This is particularly true if several lateral buds are located along the terminal shoot. Generally it is desirable to maintain growing conditions (effective weed control and adequate soil fertility) favorable for the formation of at least one lateral bud per inch of terminal branch. These buds will develop into lateral branches and so increase tree density. If fewer buds are present /less than one per inch of terminal shoot length), the terminal shoot should be cut back to approximately 12 inches in length, with the cut made approximately 1 /2 inch above a lateral bud. Other lateral branches that extend beyond the line established from the cut ends of the terminal shoot through the ends of the lateral branches of the terminal whorl should also be cut (see Fig. 6). After the tree is about S feet tall (usually in the fifth or sixth year after planting, shearing practices should change slightly. The length of the terminal shoot should not be allowed to exceed 12 inches and in some cases should be cut shorter. This depends on the fullness and the number of lateral branches developing from the terminal whorl. It is sometimes difficult to obtain full foliage development in the tips of spruce and fir trees. Reducing the length of the terminal will thicken the tree as lateral branch development continues throughout the tree and lateral buds and twigs of the terminal whorl increase in length. Little, if any, shearing of lower branches will be necessary because these tend to grow less rapidly than branches near the top of the tree. In the harvest year, only minimal shearing is required, especially for spruces. Removing competing leaders and lightly shearing the top are usually all that is necessary. Douglas fir require more Fig. 7. Correct shearing will result in a tree with straight sides deft) rather than the "bullet-shaped" tree on the right.

6 shearing because upper branches tend to grow rapidly and secondary growth flushes can result in excessively long terminal shoots. Shearing this growth back to maintain tree symmetry is usually all that is required because lower branches grow less. Some problem situations One of the challenges in shearing Christmas trees is maintaining a strong central terminal branch. This is essential to maintain good form and to produce a tree of a saleable height in the shortest time possible. Unfortunately, problem situations that require special attention frequently develop in the terminal whorl of branches. Competing terminals - This situation arises when two or more terminal branches or shoots are present. It usually develops at least once and results from the failure of any one newly formed or existing bud to assume a dominant position. Failure to cut the terminal branch at an angle during shearing increases the likelihood that multiple shoots will develop. To correct this situation, remove all but one of the competing terminals. Select the strongest branch that is most centrally located and remove the others by cutting at the base with a hand clipper, rather than a shearing knife. After the selection of a dominant terminal, the shearing process proceeds normally. No visible terminal - The opposite situation to that described above is to have a terminal whorl of branches with no one branch assuming a dominant position. This condition may result from shearing too early so that too many shoots develop or from damage to the bud that would have developed into a terminal branch. Recommended treatment is to select a strong lateral branch and allow it to become the terminal shoot. This requires cutting back all other laterals and positioning the selected lateral in a central dominant position. Some lateral branches may need to be removed entirely. Developing a dominant branch may require tying it to other shorter shoots, using a splint Fig. 8) or using commercially available terminal branch training devices. ' Damaged or broken terminal Occasionally terminal branches are damaged. Insects such as the pine shoot borer, birds (grackles find Christmas trees attractive nesting sites) and strong winds commonly cause breakage or injury. Two approaches are suggested for correcting such problems. If only the upper portion of the terminal has been damaged, it should be cut immediately below the point where the damage begins. For pines, if this is done early in 'err the summer, new buds will form at this point from which growth will occur the following year. Whether the laterals in the terminal whorl should be sheared depends on how long the terminal branch is. An alternative is to select a vigorous lateral branch and either splint or tie it to the base of the damaged terminal so that it develops into the terminal position. For species such as firs and spruces, the bud left for the terminal branch may not develop or the terminal bud on non-sheared trees will fail to grow. In this case, a lateral branch farther down the terminal shoot can be trained to assume the terminal position. To do this, select a vigorous lateral shoot and tie the base of it to the main stem so it is placed in a central position. The end bud on this shoot will develop into the new terminal for the tree. Another approach is to tie two opposite laterals together at the base so they are vertical. After tying, cut the weaker one immediately above the point of tying. This technique works best in midsummer when newly developed branches are still relatively flexible. Strong lateral competing for terminal position In some species, notably Scotch pine, it is not uncommon for a lateral shoot formed the previous year to assume a strong dominant position and compete with the current year's terminal for the terminal position. Usually this shoot should be removed at its point of origin; however, it may sometimes be desirable to leave it and remove the current season's terminal whorl of branches. This Fig 8. A small bamboo stake can be used as a splint to train a lateral branch to become a terminal leader.

7 recommendation is appropriate when growth on the original terminal is weak or, more commonly, crooked. This situation and the resulting need to select a new terminal branch are more common on some varieties of Scotch pine than others. Conclusion Shearing Christmas trees is probably the single most important process that affects tree quality. Correct shearing, together with excellent cultural practices -including effective weed control, maintenance of adequate fertility, and control of damaging insect and/or disease problems - will help assure the production of high quality trees that will be competitive in today's marketplace. North Central Regional Extension Publications are subject to peer review and prepared as a part of the Cooperative Extension activities of the thirteen land-grant universities of the 12 North Central states, in cooperation with the Extension Service-U.S. Department of Agriculture, Washington, D.C. The following states cooperated in making this publication available. University of Illinois Iowa State University *Michigan State University Ag. Publication Office 112 Printing & Publ. Bldg. Room 10B Ag Hall 69 Mumford Hall Ames, IA East Lansing, MI Urbana, IL *Publishing state For copies of this and other North Central Regional Extension publications, write to: Publications Office, Cooperative Extension Service, in care of the university listed above for your state. If they do not have copies or your state is not listed above, contact the publishing state as specified. M.R. Knelling Department of Forestry Michigan State University Programs and activities of the Cooperative Extension Service are available to all potential clientele without regard to race, color, sex, national origin, religion, age and handicap. In cooperation with NCR Educational Materials Project Issued in furtherance of Cooperative Extension work, Acts of Congress of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture and Cooperative Extension Services of Illinois and Iowa, Michael J. Tate, Interim Director, Cooperative Extension Service, Michigan State University, East Lansing, Michigan March 1991 New 3:91-7M-LKJ-Mb, Price 550, for sale only, FILE: (Forestry)

Shearing Recommendations

How many inches should a tree be cut?

What do lateral branches do to the trunk?

What process directs the shape of the tree?